Modern Masters water base Metallic paints are The Alternative to Ordinary. Easy to use, easy to clean up. By all means, use the extender to push the dry times a little father and avoid streaking. You still have to work quickly though, it is difficult to get a smooth finish on a really big area. For those spraying may be the best way, or use several people to apply at once.
I recommend you use the clear over the finish. It gives you a much better finish than without the clear.